@peaceridge: I *did* reply. Or at least I thought I did. I must have closed the browser window before clicking the submit button.
That update changed nothing in CC's network connection stuff. That leads me to think that the change is on the computer running calibre or on your network. Did you update calibre? Did you update your antivirus? Have you checked the firewall to be sure that the CC port (usually 9090) is still allowed, or if on Windows that calibre itself (Command line interface for calibre ...) is still marked as "private" (see section 1 of
How do I setup Calibre Companion to connect to calibre?)? Have you changed your wifi router?
If you are running windows then a test you can make is to start your computer in "safe mode", start calibre, then try to connect. If this works then you know for certain that something on the computer running calibre is blocking connections. See section 7 of
How do I setup Calibre Companion to connect to calibre?